Method for preparing conjugated diene-based polymer

ABSTRACT

The present invention provides a method for preparing a conjugated diene-based polymer including preparing a mixture of a molecular weight modifier and a conjugated diene-based monomer; and polymerization reacting the mixture using a catalyst composition including a lanthanide rare earth element-containing compound, modified methylaluminoxane, a halogen compound and an aliphatic hydrocarbon-based solvent, and therefore, capable of preparing a conjugated diene-based polymer having a high cis-1,4-bond content ratio, high linearity and narrow molecular weight distribution.

FIELD OF THE INVENTION

This application claims priority to and the benefits of Korean PatentApplication No. 10-2014-162932 filed with the Korean IntellectualProperty Office on Nov. 20, 2014, and Korean Patent Application No.10-2015-161322, filed with the Korean Intellectual Property Office onNov. 17, 2015, the entire contents of which are incorporated herein byreference.

The present invention relates to a method for preparing a conjugateddiene-based polymer.

DESCRIPTION OF THE RELATED ART

With increasing demands for rubber compositions in various manufacturingfields such as tires, shoe soles or golf balls, values of conjugateddiene-based polymers, particularly butadiene-based polymers among these,which are synthetic rubber, have increased as a substitute for naturalrubber that faces product shortfall.

Generally, linearity or branching of conjugated diene-based polymersgreatly affects physical properties of polymers. Specifically, meltingrates and viscosity properties of polymers increase as linearitydecreases and branching increases, and as a result, polymerprocessibility is enhanced. However, when branching of polymers is high,molecular weight distribution becomes wide, and mechanical properties ofthe polymers affecting abrasion resistance, crack resistance, a reboundproperty or the like of a rubber composition decline.

In addition, linearity or branching of conjugated diene-based polymers,particularly butadiene-based polymers, is greatly influenced by thecontent of cis-1,4 bonds included in the polymer. Linearity increases ascis-1,4 bond content in a conjugated diene-based polymer increases, andas a result, the polymer has excellent mechanical properties and mayenhance abrasion resistance, crack resistance and a rebound property ofa rubber composition.

Accordingly, various methods for preparing a conjugated diene-basedpolymer having suitable processibility while increasing linearity byincreasing cis-1,4 bond content in the conjugated diene-based polymerhave been researched and developed.

Specifically, a method using a polymerization system including alanthanide rare earth element-containing compound, particularly aneodymium-based compound, has been proposed. However, conjugateddiene-based polymers prepared through the method using thepolymerization system do not have high cis-1,4 bond content, andtherefore, physical property improving effects of a rubber compositionwere not sufficient.

In addition, a method for preparing a conjugated diene-based polymer bypreforming a catalyst composition including an organic aluminumcompound, a halogen compound and butadiene together with aneodymium-based compound, and carrying out a polymerization reaction ofa conjugated diene-based monomer using the same has been proposed.

However, the method normally uses diisobutylaluminum hydride (DIBAH) asan aluminum-based compound capable of performing a scavenger role aswell as alkylation and molecular weight modification, and DIBAH includedin a catalyst composition causes various problems during processes whenpreparing a conjugated diene-based polymer. In detail, in theabove-mentioned method, preforming is carried out adding a small amountof butadiene in order to reduce the production of various activecatalyst species in the alkylation step using DIBAH, and herein, aproblem of processibility decline occurs by polymers produced throughthe preforming of butadiene blocking a catalyst input line of apolymerization reactor. In addition, there is a problem in thatmolecular weights are not readily modified in the method, and it takeslong until changes in the molecular weight modification are identified.Particularly, conjugated diene-based polymers having many short chainbranches and low linearity, that is, having an −S/R (stress/relaxation)value of less than 1 at 100° C. are prepared since chain transfer oftenoccurs during the polymerization reaction in the above-mentioned method.However, conjugated diene-based polymers having an −S/R value of lessthan 1 as above have a problem in that resistance properties,particularly rolling resistance (RR), of a rubber composition increasesdue to a high degree of branching, and fuel efficiency propertiesdecline as a result.

In view of the above, development of methods capable of preparingconjugated diene-based polymers having high linearity throughuniformization of active catalyst species and quick and simple molecularweight modification has been required.

DISCLOSURE OF THE INVENTION Technical Problem

An object of the present invention is to provide a preparation methodcapable of preparing a conjugated diene-based polymer having a highcis-1,4-bond content ratio, high linearity and narrow molecular weightdistribution.

Technical Solution

In view of the above, one aspect of the present invention provides amethod for preparing a conjugated diene-based polymer includingpreparing a mixture of a molecular weight modifier and a conjugateddiene-based monomer; and polymerization reacting the mixture using acatalyst composition including a lanthanide rare earthelement-containing compound, modified methylaluminoxane (MAO), a halogencompound and an aliphatic hydrocarbon-based solvent.

Another aspect of the present invention provides a conjugateddiene-based polymer prepared using the method described above, andhaving 95% or higher cis-1,4-bond content.

Advantageous Effects

A method for preparing a conjugated diene-based polymer of the presentinvention does not cause problems such as reactant supply line blockageduring a process by using a catalyst composition exhibiting highcatalytic activity due to constituent premixing, is capable of quicklyand readily modifying molecular weights by introducing a molecularweight modifier alone, and is capable of preparing a conjugateddiene-based polymer having a high cis-1,4-bond content ratio, highlinearity and narrow molecular weight distribution by producing uniformactive catalyst species.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in more detail inorder to illuminate the present invention. Terms or words used in thepresent specification and the claims are not to be interpreted limitedlyto common or dictionary definitions, and shall be interpreted asmeanings and concepts corresponding to technological ideas of thepresent invention based on a principle in which the inventors maysuitably define the concepts of terms in order to describe the inventionin the best possible way.

A term “preforming” used in the present specification meanspre-polymerization in a catalyst composition for conjugated diene-basedpolymer preparation. Specifically, when a catalyst composition includinga lanthanide rare earth element-containing compound, an aluminumcompound and a halogen compound includes diisobutylaluminum hydride(DIBAH) as the aluminum compound, the catalyst composition also includesa small amount of monomers such as butadiene in order to reduce thepossibility of various active catalyst species production. Accordingly,pre-polymerization of monomers such as butadiene is carried out in thecatalyst composition for conjugated diene-based polymer preparationprior to a polymerization reaction for preparing a conjugateddiene-based polymer, and this is referred to as preforming.

In addition, a term “premixing” used in the present specification meansa state in which each constituent is uniformly mixed in a catalystcomposition without being polymerized.

A method for preparing a conjugated diene-based polymer according to oneembodiment of the present invention includes preparing a mixture of amolecular weight modifier and a conjugated diene-based monomer (step 1);and polymerization reacting the mixture using a catalyst compositionincluding a lanthanide rare earth element-containing compound; modifiedmethylaluminoxane (MMAO); a halogen compound; and an aliphatichydrocarbon-based solvent (step 2).

Existing catalyst systems for preparing a conjugated diene-based polymerare prepared by preforming a catalyst composition including a lanthaniderare earth element-containing compound, an aluminum compound such asdiisobutylaluminum hydride (hereinafter, referred to as DIBAH), ahalogen compound and butadiene. However, as described above, molecularweight is not readily modified when preparing a conjugated diene-basedpolymer using such a catalyst system, and it takes long until changes inthe molecular weight modification are identified. In addition, a problemof polymers produced by butadiene preforming blocking a catalyst inputline of a polymerization reactor occurs during a process.

In view of the above, the present invention uses modifiedmethylaluminoxane (hereinafter, referred to as ‘MAO’) instead of analuminum-based compound such as DIBAH used to be used for producinguniform active catalyst species in conjugated diene-based catalystcomposition preparation, and accordingly, there is no concern forproblems during a process, and superior catalytic activity is obtainedsince aliphatic hydrocarbon-based solvents may be used instead ofcommonly used aromatic hydrocarbon-based solvents. In addition, byintroducing an aluminum-based compound including DIBAH alone separatelyfrom the catalyst composition when preparing a conjugated diene-basedpolymer using the same, uniform active catalyst species are capable ofbeing produced, molecular weights are readily modified, and as a result,a conjugated diene-based polymer having high linearity may be prepared.

When examining each step, the step 1 in the method for preparing aconjugated diene-based polymer according to one embodiment of thepresent invention is a step of preparing a mixture of a molecular weightmodifier and a conjugated diene-based monomer.

As described above, in the method for preparing a conjugated diene-basedpolymer according to one embodiment of the present invention, amolecular weight modifier is separately mixed with a conjugateddiene-based monomer instead of being introduced to a catalystcomposition as in existing methods for preparing a conjugateddiene-based polymer, and therefore, the molecular weight may be quicklymodified in a conjugated diene-based polymer production process, whichleads to processibility improvement.

In the step 1, organic aluminum compounds may be used as the molecularweight modifier.

Specific examples of the organic aluminum compound includetrihydrocarbylaluminum such as trimethylaluminum, triethylaluminum,triisobutylaluminum, tri-n-propylaluminum, triisopropylaluminum,tri-n-butylaluminum, tri-t-butylaluminum, tri-n-pentylaluminum,trineopentylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum,tris(2-ethylhexyl)aluminum, tricyclohexylaluminum,tris(1-methylcyclopentyl)aluminum, triphenylaluminum,tri-p-tolylaluminum, tris(2,6-dimethylphenyl)aluminum,tribenzylaluminum, diethylphenylaluminum, diethyl-p-tolylaluminum,diethylbenzylaluminum, ethyldiphenylaluminum, ethyldi-p-tolylaluminum orethyldibenzylaluminum; or dihydrocarbylaluminum hydride such asdimethylaluminum hydride, diethylaluminum hydride, di-n-propylaluminumhydride, diisopropylaluminum hydride, di-n-butylaluminum hydride,diisobutylaluminum hydride (DIBAH), di-t-butylaluminum hydride,dipentylaluminum hydride, dihexylaluminum hydride, dicyclohexylaluminumhydride or dioctylaluminum hydride, and any one or a mixture of two ormore of these may be used.

In addition, as the molecular weight modifier, hydrogen; or silanecompounds such as trimethyl silane, triethyl silane, tributyl silane,trihexyl silane, dimethyl silane, diethyl silane, dibutyl silane ordihexyl silane may be used. The silane compound may be used alone as themolecular weight modifier, or may be mixed with the organic aluminumcompound described above. When considering superiority of improvingeffects by the use of a molecular weight modifier, the molecular weightmodifier may be diethylaluminum hydride, diisobutylaluminum hydride(DIBAH) or a mixture thereof among the above-mentioned compounds, andmore specifically, may be diisobutylaluminum hydride. The molecularweight modifier not only modifies molecular weights but may act as ascavenger, and therefore, the amount of the molecular weight modifierused may vary depending on the amount of impurities and the amount ofmoisture. Specifically, in the preparation method according to oneembodiment of the present invention, the content of the molecular weightmodifier capable of being used in the step 1 may be from 1 mol to 100mol with respect to 1 mol of the lanthanide rare earthelement-containing compound.

Meanwhile, in the step 1, the use of the monomer is not particularlylimited as long as the monomer is commonly used in conjugateddiene-based polymer preparation. Specifically, the monomer may include1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,2-ethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 1,3-pentadiene,3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, 1,3-hexadiene,2,4-hexadiene or the like, and more specifically, may be 1,3-butadieneor derivatives thereof such as 1,3-butadiene, isoprene,2,3-dimethyl-1,3-butadiene or 2-ethyl-1,3-butadiene, and any one or amixture of two or more of these may be used.

In addition, with the monomer, other monomers copolymerizable with themonomer may be selectively used. Herein, the other monomer additionallyused may be used in proper content considering physical properties of afinally prepared conjugated diene-based polymer.

Specific examples of the other monomer may include aromatic vinylmonomers such as styrene, p-methylstyrene, α-methylstyrene,1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene,4-cyclohexylstyrene and 2,4,6-trimethylstyrene, and any one or a mixtureof two or more of these may be used. The other monomer may be used inthe content of 20% by weight or less with respect to the total monomerweight used in a polymerization reaction for preparing a conjugateddiene-based polymer.

In addition, in the method for preparing a conjugated diene-basedpolymer according to one embodiment of the present invention, the step 2is a step polymerization reacting the mixture prepared in the step 1using a catalyst composition including a lanthanide rare earthelement-containing compound, modified methylaluminoxane (MMAO), ahalogen compound and an aliphatic hydrocarbon-based solvent.

In the step 2, the catalyst composition is a pre-mixture of thelanthanide rare earth element-containing compound, the MMAO, the halogencompound and the aliphatic hydrocarbon-based solvent, and may beprepared by mixing the above-mentioned compounds using common methods.

As described above, in the method for preparing a conjugated diene-basedpolymer according to one embodiment of the present invention, thecatalyst composition does not include diisobutylaluminum hydride (DIBAH)unlike existing catalyst compositions for preparing a conjugateddiene-based polymer, and premixing instead of preforming is carried out,and therefore, it is very advantageous in terms of a process such thatblockage of polymerization reactor catalyst input line by polymerscaused by existing butadiene preforming may be prevented.

Specifically, in the catalyst composition, the lanthanide rare earthelement-containing compound may be a compound including any one, two ormore elements among rare earth elements of atomic numbers 57 to 71 inthe periodic table such as neodymium, praseodymium, cerium, lanthanum orgadolinium, and more specifically, a compound including neodymium.

In addition, the lanthanide rare earth element-containing compound maybe a salt soluble in a hydrocarbon solvent such as carboxylates,alkoxides, β-diketone complexes, phosphates or phosphites of lanthaniderare earth elements, and more specifically, may be theneodyminum-containing carboxylates. The hydrocarbon solvent may besaturated aliphatic hydrocarbon having 4 to carbon atoms such as butane,pentane, hexane and heptane; saturated alicyclic hydrocarbon having 5 to20 carbon atoms such as cyclopentane and cyclohexane;

monoolefins such as 1-butene and 2-butene; aromatic hydrocarbon such asbenzene, toluene and xylene; or halogenated hydrocarbon such asmethylene chloride, chloroform, trichloroethylene, perchloroethylene,1,2-dichloroethane, chlorobenzene, bromobenzene or chlorotoluene.

More specifically, the lanthanide rare earth element-containing compoundmay be a neodymium compound of the following Chemical Formula 1:

in Chemical Formula 1,

R₁ to R₃ are each independently a hydrogen atom or a linear or branchedalkyl group having 1 to 12 carbon atoms.

Specifically, the neodymium compound may be any one or a mixture of twoor more selected from the group consisting of Nd(neodecanoate)₃,Nd(2-ethylhexanoate)₃, Nd(2,2-diethyl decanoate)₃, Nd(2,2-dipropyldecanoate)₃, Nd(2,2-dibutyl decanoate)₃, Nd(2,2-dihexyl decanoate)₃,Nd(2,2-dioctyl decanoate)₃, Nd(2-ethyl-2-propyl decanoate)₃,Nd(2-ethyl-2-butyl decanoate)₃, Nd(2-ethyl-2-hexyl decanoate)₃,Nd(2-propyl-2-butyl decanoate)₃, Nd(2-propyl-2-hexyl decanoate)₃,Nd(2-propyl-2-isopropyl decanoate)₃, Nd(2-butyl-2-hexyl decanoate)₃,Nd(2-hexyl-2-octyl decanoate)₃, Nd(2-t-butyl decanoate)₃, Nd(2,2-diethyloctanoate)₃, Nd(2,2-dipropyl octanoate)₃, Nd(2,2-dibutyl octanoate)₃,Nd(2,2-dihexyl octanoate)₃, Nd(2-ethyl-2-propyl octanoate)₃,Nd(2-ethyl-2-hexyl octanoate)₃, Nd(2,2-diethyl nonanoate)₃,Nd(2,2-dipropyl nonanoate)₃, Nd(2,2-dibutyl nonanoate)₃, Nd(2,2-dihexylnonanoate)₃, Nd(2-ethyl-2-propyl nonanoate)₃ and Nd(2-ethyl-2-hexylnonanoate)₃.

In addition, when considering excellent solubility for polymerizationsolvents without concern for oligomerization, a rate of conversion to anactive catalyst species and superiority of catalytic activity improvingeffects obtained therefrom, the lanthanide rare earth element-containingcompound may more specifically be a neodymium compound in which, inChemical Formula 1, R₁ is a linear or branched alkyl group having 6 to12 carbon atoms or 6 to 8 carbon atoms, and R₂ and R₃ are eachindependently a hydrogen atom or a linear or branched alkyl group having2 to 8 carbon atoms, but R₂ and R₃ are not both hydrogen atoms at thesame time. Specific examples thereof may include Nd(2,2-diethyldecanoate)₃, Nd(2,2-dipropyl decanoate)₃, Nd(2,2-dibutyl decanoate)₃,Nd(2,2-dihexyl decanoate)₃, Nd(2,2-dioctyl decanoate)₃,Nd(2-ethyl-2-propyl decanoate)₃, Nd(2-ethyl-2-butyl decanoate)₃,Nd(2-ethyl-2-hexyl decanoate)₃, Nd(2-propyl-2-butyl decanoate)₃,Nd(2-propyl-2-hexyl decanoate)₃, Nd(2-propyl-2-isopropyl decanoate)₃,Nd(2-butyl-2-hexyl decanoate)₃, Nd(2-hexyl-2-octyl decanoate)₃,Nd(2-t-butyl decanoate)₃, Nd(2,2-diethyl octanoate)₃, Nd(2,2-dipropyloctanoate)₃, Nd(2,2-dibutyl octanoate)₃, Nd(2,2-dihexyl octanoate)₃,Nd(2-ethyl-2-propyl octanoate)₃, Nd(2-ethyl-2-hexyl octanoate)₃,Nd(2,2-diethyl nonanoate)₃, Nd(2,2-dipropyl nonanoate)₃, Nd(2,2-dibutylnonanoate)₃, Nd(2,2-dihexyl nonanoate)₃, Nd(2-ethyl-2-propyl nonanoate)₃Nd(2-ethyl-2-hexyl nonanoate)₃, or the like, and among these, theneodymium compound may be any one or a mixture of two or more selectedfrom the group consisting of Nd(2,2-diethyl decanoate)₃, Nd(2,2-dipropyldecanoate)₃, Nd(2,2-dibutyl decanoate)₃, Nd(2,2-dihexyl decanoate)₃ andNd(2,2-dioctyl decanoate)₃.

Even more specifically, the lanthanide rare earth element-containingcompound may be a neodymium compound in which, in Chemical Formula 1, R₁is a linear or branched alkyl group having 6 to 8 carbon atoms, R₂ andR₃ are each independently a linear or branched alkyl group having 2 to 8carbon atoms.

Thus, when the neodymium compound of Chemical Formula 1 includes acarboxylate ligand including an alkyl group with various lengths of 2 ormore carbon atoms as a substituent at an a position, coagulation betweenthe compounds may be blocked by inducing stereoscopic changes around theneodymium central metal, and as a result, oligomerization may besuppressed. In addition, such a neodymium compound has high solubilityfor polymerization solvents, and has a high rate of conversion to anactive catalyst species since the ratio of neodymium located in thecentral part having difficulties in being converted to an activecatalyst species decreases.

Furthermore, the neodymium compound of Chemical Formula 1 may havesolubility of approximately 4 g or greater per 6 g of a non-polarsolvent at room temperature (20±5° C.). In the present invention,solubility of the neodymium compound means a level of being clearlydissolved without turbidity. By having such high solubility, excellentcatalytic activity may be obtained.

Meanwhile, in the catalyst composition, the modified methylaluminoxanefunctions as an alkylating agent in the catalyst composition in place ofexisting DIBAH. The modified methylaluminoxane is a compoundsubstituting a methyl group of methylaluminoxane with a modificationgroup, specifically, a hydrocarbon group having 2 to 20 carbon atoms,and may specifically be a compound of the following Chemical Formula 2:

in Chemical Formula 2, R is a hydrocarbon group having 2 to 20 carbonatoms, m and n are each an integer of 2 or greater. In addition, Me inChemical Formula 2 means a methyl group.

More specifically, R in Chemical Formula 2 may be a linear or branchedalkyl group having 2 to 20 carbon atoms, a cycloalkyl group having 3 to20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, acycloalkenyl group having 3 to 20 carbon atoms, an aryl group having 6to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms, analkylaryl group having 7 to 20 carbon atoms, an allyl group, or analkynyl group having 2 to 20 carbon atoms, and more specifically, alinear or branched alkyl group having 2 to 10 carbon atoms such as anethyl group, an isobutyl group, a hexyl group or an octyl group, andeven more specifically an isobutyl group.

Even more specifically, the modified methylaluminoxane may be a compoundsubstituting approximately 50 mol % or more of a methyl group of themethylaluminoxane, more specifically 50 mol % to 90 mol %, with ahydrocarbon group having 2 to 20 carbon atoms. When the content of thesubstituted hydrocarbon group in the modified methylaluminoxane is inthe above-mentioned range, alkylation is facilitated and as a result,catalytic activity may increase.

Such modified methylaluminoxane may be prepared using common methods,and specifically, may be prepared using trimethylaluminum, and atrialkylaluminum other than trimethylaluminum. Herein, thetrialkylaluminum may be triisobutylaluminum, triethylaluminum,trihexylaluminum, trioctylaluminum or the like, and any one or a mixtureof two or more of these may be used. In this case, the modifiedmethylaluminoxane may include trimethylaluminum; and a mixed alkyl groupderived from one or more types of trialkylaluminums other thantrimethylaluminum, and the trialkylaluminum may include any one or amixture of two or more types selected from the group consisting oftriisobutylaluminum, triethylaluminum, trihexylaluminum andtrioctylaluminum.

With alkylaluminoxane such as methylaluminoxane (MAO) orethylaluminoxane commonly used for conjugated diene polymer preparation,aromatic hydrocarbon-based solvents need to be used sincealkylaluminoxane is not readily dissolved in aliphatic hydrocarbon-basedsolvents. However, aromatic hydrocarbon-based solvents have a problem ofreducing reactivity, and when mixing an aromatic hydrocarbon-basedsolvent and an aliphatic hydrocarbon-based solvent in a catalyst system,there is a problem of reducing catalytic activity. However, in thepresent invention, modified methylaluminoxane capable of being readilydissolved in aliphatic hydrocarbon-based solvents is used, andaccordingly, a single solvent system with an aliphatic hydrocarbon-basedsolvent such as hexane that is normally used as a polymerization solventis capable of being used, which is more advantageous for apolymerization reaction. In addition, an aliphatic hydrocarbon-basedsolvent may facilitate catalytic activity, and reactivity may be furtherenhanced by such catalytic activity. As a result, molecular weights maybe quickly and readily modified, and polymerization is favorablyprogressed even at low temperatures due to very high catalytic activity,and time for polymerization reaction may be reduced even with a smallmain catalyst amount.

In addition, in the catalyst composition, specific examples of thealiphatic hydrocarbon-based solvent may include a mixed solvent of alinear, branched or cyclic aliphatic hydrocarbon-based solvent having 5to 20 carbon atoms such as n-pentane, n-hexane, n-heptane, n-octane,n-nonane, n-decane, isopentane, isohexane, isoheptane, isooctane,2,2-dimethylbutane, cyclopentane, cyclohexane, methylcyclopentane ormethylcyclohexane; or aliphatic hydrocarbon having 5 to 20 carbon atomssuch as petroleum ether (or petroleum spirits) or kerosene, and any oneor a mixture of two or more of these may be used. Among these, whenconsidering excellent solubility for modified methylaluminoxane andsuperiority of catalytic activity improving effects resulted therefrom,the aliphatic hydrocarbon-based solvent may be a linear, branched orcyclic aliphatic hydrocarbon-based solvent having 5 to 8 carbon atoms,or a mixture thereof, and more specifically n-hexane, cyclohexane, or amixture thereof.

Furthermore, in the catalyst composition, the types of the halogencompound are not particularly limited, and those commonly used ashalogenides in diene-based polymer preparation may be used withoutparticular limit. Specifically, the halogen compound may includeelemental halogen compounds, interhalogen compounds, halogenatedhydrogen, organic halides, non-metal halides, metal halides, organicmetal halides or the like, and any one or a mixture of two or more ofthese may be used. Among these, when considering catalytic activityenhancement and superiority of reactivity improving effects resultedtherefrom, any one or a mixture of two or more selected from the groupconsisting of organic halides, metal halides and organic metal halidesmay be used as the halogen compound.

More specifically, the elemental halogen compound may include diatomicmolecular compounds such as fluorine (F₂), chlorine (Cl₂), bromine (Br₂)or iodine (I₂).

Specific examples of the interhalogen compound may include iodinemonochloride, iodine monobromide, iodine trichloride, iodinepentafluoride, iodine monofluoride, iodine trifluoride or the like.

In addition, specific examples of the halogenated hydrogen may includehydrogen fluoride, hydrogen chloride, hydrogen bromide, hydrogen iodideor the like.

Specific examples of the organic halide may include t-butyl chloride,t-butyl bromide, allyl chloride, allyl bromide, benzyl chloride, benzylbromide, chloro-di-phenylmethane, bromo-di-phenylmethane,triphenylmethyl chloride, triphenylmethyl bromide, benzylidene chloride,benzyliene bromide, methyltrichlorosilane, phenyltrichlorosilane,dimethyldichlorosilane, diphenyldichlorosilane, trimethylchlorosilane,benzoyl chloride, benzoyl bromide, propionyl chloride, propionylbromide, methyl chloroformate, methyl bromoformate, iodomethane,diiodomethane, triiodomethane (also called as ‘iodoform’),tetraiodomethane, 1-iodopropane, 2-iodopropane, 1,3-diiodopropane,t-butyl iodide, 2,2-dimethyl-1-iodopropane (also called as ‘neopentyliodide’), allyl iodide, iodobenzene, benzyl iodide, diphenylmethyliodide, triphenylmethyl iodide, benzylidene iodide (also called as‘benzal iodide’), trimethylsilyl iodide, triethylsilyl iodide,triphenylsilyl iodide, dimethyldiiodosilane, diethyldiiodosilane,diphenyldiiodosilane, methyltriiodosilane, ethyltriiodosilane,phenyltriiodosilane, benzoyl iodide, propionyl iodide, methyliodoformate or the like.

Specific examples of the non-metal halide may include phosphoroustrichloride, phosphorous tribromide, phosphorous pentachloride,phosphorous oxychloride, phosphorous oxybromide, boron trifluoride,boron trichloride, boron tribromide, silicon tetrafluoride, silicontetrachloride, silicon tetrabromide, arsenic trichloride, arsenictribromide, selenium tetrachloride, selenium tetrabromide, telluriumtetrachloride, tellurium tetrabromide, silicon tetraiodide, arsenictriiodide, tellurium tetraiodide, boron triiodide, phosphoroustriiodide, phosphorous oxyiodide, selenium tetraiodide or the like.

Specific examples of the metal halide may include tin tetrachloride, tintetrabromide, aluminum trichloride, aluminum tribromide, antimonytrichloride, antimony pentachloride, antimony tribromide, aluminumtrifluoride, gallium trichloride, gallium tribromide, galliumtrifluoride, indium trichloride, indium tribromide, indium trifluoride,titanium tetrachloride, titanium tetrabromide, zinc dichloride, zincdibromide, zinc difluoride, aluminum triiodide, gallium triiodide,indium triiodide, titanium tetraiodide, zinc diiodide, germaniumtetraiodide, tin tetraiodide, tin diiodide, antimony triiodide ormagnesium diiodide.

Specific examples of the organic metal halide may includedimethylaluminum chloride, diethylaluminum chloride, dimethylaluminumbromide, diethylaluminum bromide, dimethylaluminum fluoride,diethylaluminum fluoride, methylaluminum dichloride, ethylaluminumdichloride, methylaluminum dibromide, ethylaluminum dibromide,methylaluminum difluoride, ethylaluminum difluoride, methylaluminumsesquichloride, ethylaluminum sesquichloride, isobutylaluminumsesquichloride, methylmagnesium chloride, methylmagnesium bromide,ethylmagnesium chloride, ethylmagnesium bromide, n-butylmagnesiumchloride, n-butylmagnesium bromide, phenylmagnesium chloride,phenylmagnesium bromide, benzylmagnesium chloride, trimethyltinchloride, trimethyltin bromide, triethyltin chloride, triethyltinbromide, di-t-butyltin dichloride, di-t-butyltin dibromide,di-n-butyltin dichloride, di-n-butyltin dibromide, tri-n-butyltinchloride, tri-n-butyltin bromide, methylmagnesium iodide,dimethylaluminum iodide, diethylaluminum iodide, di-n-butylaluminumiodide, diisobutylaluminum iodide, di-n-octylaluminum iodide,methylaluminum diiodide, ethylaluminum diiodide, n-butylaluminumdiiodide, isobutylaluminum diiodide, methylaluminum sesquiiodide,ethylaluminum sesquiiodide, isobutylaluminum sesquiiodide,ethylmagnesium iodide, n-butylmagnesium iodide, isobutylmagnesiumiodide, phenylmagnesium iodide, benzylmagnesium iodide, trimethyltiniodide, triethyltin iodide, tri-n-butyltin iodide, di-n-butyltindiiodide, di-t-butyl tin diiodide or the like.

The catalyst composition according to one embodiment of the presentinvention may include the above-mentioned constituents in optimumcontent so as to exhibit more superior catalytic activity in apolymerization reaction for forming a conjugated diene-based polymer.

Specifically, the catalyst composition may include the lanthanide rareearth element-containing compound in an amount of 0.01 mmol to 0.25mmol, specifically in 0.02 mmol to 0.20 mmol and more specifically in0.02 mmol to 0.10 mmol with respect to 100 g of the conjugateddiene-based monomer.

In addition, the catalyst composition may include the modifiedmethylaluminoxane in a molar ratio of 5 to 200 and more specifically ina molar ratio of 10 to 100 with respect to 1 mol of the lanthanide rareearth element-containing compound.

In addition, the catalyst composition may include the halogen compoundin a molar ratio of 1 to 10 and more specifically in a molar ratio of 2to 6 with respect to 1 mol of the lanthanide rare earthelement-containing compound.

Furthermore, the catalyst composition may include the aliphatichydrocarbon-based solvent in a molar ratio of 20 to 20,000 and morespecifically in a molar ratio of 100 to 1,000 with respect to 1 mol ofthe lanthanide rare earth element-containing compound.

More specifically, when considering superiority of catalytic activityfor a polymerization reaction of a conjugated diene-based polymer, thecatalyst composition according to one embodiment of the presentinvention is a pre-mixture including, with respect to 1 mol of thelanthanide rare earth element-containing compound, the modifiedmethylaluminoxane in 5 mol to 200 mol, the halogen compound in 1 mol to10 mol and the aliphatic hydrocarbon-based solvent in 20 mol to 20,000mol.

According to another embodiment of the present invention, the catalystcomposition includes the lanthanide rare earth element-containingcompound in an amount of 0.01 mmol to 0.25 mmol, the modifiedmethylaluminoxane in 0.1 mmol to 25.0 mmol, the halogen compound in 0.02mmol to 1.5 mmol, and the aliphatic hydrocarbon-based solvent in 10 mmolto 180 mmol with respect to 100 g of the conjugated diene-based monomer.

More specifically, the catalyst composition includes the lanthanide rareearth element-containing compound in an amount of 0.01 mmol to 0.05mmol, the modified methylaluminoxane in 0.1 mmol to 5.0 mmol, thehalogen compound in 0.03 mmol to 0.10 mmol, and the aliphatichydrocarbon-based solvent in 10 mmol to 180 mmol with respect to 100 gof the conjugated diene-based monomer.

When considering superiority of catalytic activity for a polymerizationreaction of a conjugated diene-based polymer, the catalyst compositionis a pre-mixture including the lanthanide rare earth element-containingcompound in 0.01 mmol to 0.25 mmol, the modified methylaluminoxane in0.05 mmol to 50.0 mmol, the halogen compound in 0.01 mmol to 2.5 mmol,and the aliphatic hydrocarbon-based solvent in 2 mmol to 200 mmol or 5mmol to 200 mmol with respect to 100 g of the conjugated diene-basedmonomer, and herein, the lanthanide rare earth element-containingcompound includes a neodymium compound in which, in Chemical Formula 1,R₁ is a linear or branched alkyl group having 6 to 12 carbon atoms, andR₂ and R₃ are each independently a hydrogen atom or a linear or branchedalkyl group having 2 to 6 carbon atoms, but R₂ and R₃ are not bothhydrogen atoms at the same time, and the modified methylaluminoxane is acompound substituting approximately 50 mol % or more of a methyl groupof the methylaluminoxane with a hydrocarbon group having 2 to 20 carbonatoms, and the aliphatic hydrocarbon-based solvent includes any one or amixture of two or more selected from the group consisting of linear,branched and cyclic aliphatic hydrocarbon-based solvents having 5 to 8carbon atoms.

In addition, mixing of the lanthanide rare earth element-containingcompound, the methylaluminoxane, the halogen compound and the aliphatichydrocarbon-based solvent such as above may be carried out using commonmethods. Herein, the mixing may be carried out in a temperature range of0° C. to 60° C. in order to facilitate active catalyst speciesproduction, and a heat treatment process may be combined for satisfyingthe above-mentioned temperature condition. More specifically, a mixedprocess including the steps of mixing the lanthanide rare earthelement-containing compound, the modified methylaluminoxane and thealiphatic hydrocarbon-based solvent in the above-mentioned composition,first heat treating the result at a temperature of 10° C. to 60° C., andcarrying out a second heat treatment in a temperature range of 0° C. to60° C. by introducing the halogen compound to the mixture resultantlyobtained may be carried out.

The catalyst composition having a composition as described above mayexhibit catalytic activity of 10,000 kg[polymer]/mol[Nd]h duringpolymerization of 5 minutes to 60 minutes in a temperature range of 20°C. to 90° C. The catalytic activity in the present invention is a valueobtained from a molar ratio of the lanthanide rare earthelement-containing compound, more specifically the neodymium compound ofChemical Formula 1, introduced with respect to the total yield of theprepared diene-based polymer.

Meanwhile, during the polymerization reaction in the step 2, a reactionterminating agent such as polyoxyethylene glycol phosphate, anantioxidant such as 2,6-di-t-butylparacresol, and additives such as achelating agent, a dispersion agent, a pH controlling agent, adeoxidizer or an oxygen scavenger commonly used for facilitatingsolution polymerization may be further used selectively.

In addition, the polymerization reaction in the step 2 may be carriedout in a temperature range of 20° C. to 90° C., and particularly, a 100%conversion rate of polymers is capable of being accomplished in a shorttime even at a low temperature of 20° C. to 30° C. When the temperatureexceeds 90° C. in the polymerization reaction, the polymerizationreaction is difficult to be sufficiently controlled, and there isconcern that cis-1,4 bond content of the produced diene-based polymermay decrease. When the temperature is less than 20° C., there is concernthat polymerization reaction rate and efficiency may decrease.

Furthermore, according to the preparation method according to oneembodiment of the present invention, the polymerization reaction may becarried out for 5 minutes to 60 minutes until the reaction reaches 100%conversion to the conjugated diene-based polymer, and specifically, maybe carried out for 10 minutes to 30 minutes.

In addition, after the reaction is complete, the prepared conjugateddiene-based polymer may be obtained by adding lower alcohols such asmethyl alcohol or ethyl alcohol, or steam for precipitation.Accordingly, the method for preparing a conjugated diene-based polymeraccording to one embodiment of the present invention may further includeprecipitation and separation processes for a conjugated diene-basedpolymer prepared after the polymerization reaction. Herein, filtering,separating and drying processes for the conjugated diene-based polymermay be carried out using common methods.

According to the preparation method such as above, a conjugateddiene-based polymer, specifically, a neodymium-catalyzed conjugateddiene-based polymer including an active organic metal site derived froma catalyst including the lanthanide rare earth element-containingcompound, more specifically the neodymium compound of Chemical Formula1, and even more specifically, neodymium-catalyzed 1,4-cis polybutadieneincluding a 1,3-butadiene monomer unit is produced. In addition, theconjugated diene-based polymer may be 1,4-cis polybutadiene formed onlywith a 1,3-butadiene monomer.

In addition, the conjugated diene-based polymer prepared using theabove-mentioned preparation method has excellent physical propertiesincluding high linearity as described above.

Specifically, the conjugated diene-based polymer is a polymer havinghigh linearity with a −S/R (stress/relaxation) value of 1 or greater at100° C. More specifically, a −S/R value of the conjugated diene-basedpolymer is from 1 to 1.2, and even more specifically from 1.045 to 1.2.

In the present invention, the −S/R value represents changes in stressshown as a reaction for the same amount of strain generated in amaterial, and is an index representing polymer linearity. A lower −S/Rvalue commonly means lower conjugated diene-based polymer linearity, andas linearity decreases, rolling resistance increases when used in arubber composition. In addition, a degree of branching and molecularweight distribution may be predicted from the −S/R value. As the −S/Rvalue decreases, the degree of branching increases, and the molecularweight distribution becomes wider, and as a result, mechanicalproperties are poor whereas polymer processibility is superior.

By the conjugated diene-based polymer according to one embodiment of thepresent invention having the above-mentioned −S/R value range, rollingresistance (RR) decreases compared to polymers prepared using existingcatalyst systems, and an effect of greatly enhancing fuel efficiencyproperties may be obtained.

In the present invention, the −S/R value may be measured using a Mooneyviscometer, for example, a Large Rotor of MV2000E manufactured byMonsanto under a condition of 100° C. and Rotor Speed 2±0.02 rpm.Specifically, the polymer is left unattended for 30 minutes or longer atroom temperature (23±5° C.), 27±3 g thereof is collected and inside adie cavity is filled with the polymer sample, and Mooney viscosity ismeasured while operating a Platen and applying Torque, and by measuringa slope of Mooney viscosity changes appearing while releasing Torque,the −S/R value may be determined.

In addition, the conjugated diene-based polymer according to oneembodiment of the present invention may have narrow molecular weightdistribution having polydispersity (PDI) of 3 or less. When theconjugated diene-based polymer has PDI of greater than 3, there isconcern that mechanical properties such as abrasion resistance andimpact resistance decline when used in a rubber composition. Whenconsidering the significance of mechanical property improving effects ofthe polymer due to PDI control, PDI of the conjugated diene-basedpolymer may be specifically from 2.0 to 2.5, and more specifically from2.35 to 2.5.

In the present invention, PDI of a conjugated diene-based polymer isalso referred to as molecular weight distribution (MWD), and may becalculated from a ratio (Mw/Mn) of a weight average molecular weight(Mw) to a number average molecular weight (Mn). Herein, the numberaverage molecular weight (Mn) is a common average of individualmolecular weights of polymers calculated by measuring molecular weightsof n polymer molecules, and dividing the sum of these molecular weightsby n, and the weight average molecular weight (Mw) represents molecularweight distribution of a polymer composition, and may be calculated bythe following Mathematical Formula 1.

$\begin{matrix}{M_{W} = \frac{\sum\limits_{i}{N_{i}M_{i}^{2}}}{\sum\limits_{i}{N_{i}M_{i}}}} & \left\lbrack {{Mathematical}\mspace{14mu} {Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Mathematical Formula 1, Ni is the number of molecules having amolecular weight of Mi. An average of all molecular weights may berepresented by gram per mol (g/mol).

Furthermore, in the present invention, the weight average molecularweight and the number average molecular weight are each a polystyreneconverted molecular weight analyzed with gel permeation chromatography(GPC).

In addition, the conjugated diene-based polymer according to oneembodiment of the present invention may have a weight average molecularweight (Mw) of 400,000 g/mol to 2,500,000 g/mol and specifically1,100,000 g/mol to 2,300,000 g/mol while satisfying the polydispersitycondition. Furthermore, the conjugated diene-based polymer according toone embodiment of the present invention may have a number averagemolecular weight (Mn) of 100,000 g/mol to 1,000,000 g/mol andspecifically 500,000 g/mol to 900,000 g/mol. When the weight averagemolecular weight (Mw) of the conjugated diene-based polymer is less than400,000 g/mol or the number average molecular weight (Mn) is less than100,000 g/mol, there is concern of an increase in hysteresis loss due toelasticity decline of a vulcanizate, and degeneration of abrasionresistance. In addition, when the weight average molecular weight (Mw)is greater than 2,500,000 g/mol or the number average molecular weight(Mn) is greater than 1,000,000 g/mol, processibility of the conjugateddiene-based polymer declines causing degeneration in the workability ofa rubber composition, and mixing and kneading become difficult, and as aresult, physical properties of the rubber composition may be difficultto be sufficiently enhanced.

Furthermore, the conjugated diene-based polymer according to oneembodiment of the present invention may have Mooney viscosity (MV) of 30to 90 and specifically 70 to 90 at 100° C. More superior processibilitymay be obtained when the Mooney viscosity is in the above-mentionedrange.

In the present invention, Mooney viscosity may be measured using aMooney viscometer, for example, a Large Rotor of MV2000E of Monsanto at100° C. and Rotor Speed 2±0.02 rpm. Herein, the measurement may be madeby leaving the sample used unattended for 30 minutes or longer at roomtemperature (23±5° C.), collecting 27±3 g thereof, and filling inside adie cavity with the sample, and operating a Platen.

In addition, in the conjugated diene-based polymer according to oneembodiment of the present invention, cis bond content in the conjugateddiene-based polymer measured using Fourier Transform InfraredSpectroscopy, specifically cis-1,4 bond content, may be 95% or higherand more specifically 96% or higher. When the cis-1,4 bond content inthe polymer is high as above, linearity increases, and abrasionresistance and crack resistance of a rubber composition may be enhancedwhen being mixed to the rubber composition.

Accordingly, another embodiment of the present invention provides arubber composition including the conjugated diene-based polymer.

Specifically, the rubber composition may include the conjugateddiene-based polymer in 10% by weight to 100% by weight and a rubbercomponent in 0 to 90% by weight. When the content of the conjugateddiene-based polymer is less than 10% by weight, effects of improvingabrasion resistance, crack resistance and ozone resistance of the rubbercomposition may be insignificant.

In the rubber composition, the rubber component may be specificallynatural rubber (NR); or synthetic rubber such as a styrene-butadienecopolymer (SBR), hydrogen-added SBR, polybutadiene (BR) having lowcis-1,4-bond content, hydrogen-added BR, polyisoprene (IR), butyl rubber(IIR), ethylene-propylene rubber, ethylene-propylene diene rubber,polyisobutylene-co-isoprene, neoprene, poly(ethylene-co-propylene),poly(styrene-co-butadiene), poly(styrene-co-isoprene),poly(styrene-co-isoprene-co-butadiene), poly(isoprene-co-butadiene),poly(ethylene-co-propylene-co-diene), polysulfide rubber, acrylicrubber, urethane rubber, silicone rubber or epichlorohydrin rubber, andany one or a mixture of two or more of these may be used.

In addition, the rubber composition may further include a filler in 10parts by weight or greater with respect to 100 parts by weight of therubber component. Herein, the filler may be carbon black, starch,silica, aluminum hydroxide, magnesium hydroxide, clay (hydrated aluminumsilicate) and the like, and any one or a mixture of two or more of thesemay be used.

Furthermore, the rubber composition may further include, in addition tothe rubber component and the filler described above, compounding agentscommonly used in a rubber industry such as a vulcanizing agent, avulcanization accelerator, an antiaging agent, an antiscorching agent, asoftner, zinc oxide, stearic acid or silane coupling agent by properlyselecting and mixing them within a range that does not undermine anobject of the present invention.

Specifically, such a rubber composition is useful for preparing variousmolded rubber articles such as automobiles, trucks (tracks), tires forbuses (for example, tire treads, side walls, sub-treads, bead fillers,brake members and the like), elastic components of a tire stock,O-rings, profiles, gaskets, films, hoses, belts, shoe soles, cushionrubber or window seals. Particularly, by including a conjugateddiene-based polymer having high linearity with a −S/R value of 1 orgreater at 100° C., resistance properties, particularly rollingresistance, decreases, and significantly improved fuel efficiencyproperties are obtained, and as a result, the rubber composition may beuseful in tires requiring low resistance properties and excellent fuelefficiency properties.

Hereinafter, the present invention will be described in detail withreference to examples in order to specifically describe the presentinvention. However, the examples according to the present invention maybe modified to various other forms, and the scope of the presentinvention is not to be interpreted to be limited to the examplesdescribed below. The examples of the present invention are provided inorder to more completely describe the present invention for thoseskilled in the art.

[Preparation of Neodymium Compound]

PREPARATION EXAMPLE 1: SYNTHESIS OF ND(2,2-DIHEXYL DECANOATE)₃

To a 50 ml round flask having 0.35 g (1.0 mmol) of 2,2-dihexyl decanoicacid therein, 10 ml of ethanol was added, and the result was stirred for10 minutes at room temperature (20±5° C.). 1.0 ml of a 1.0 M aqueoussodium hydroxide solution (1.0 mmol) was added to the mixed solutionobtained as a result, and the result was stirred for 1 hour at roomtemperature (20±5° C.) to prepare a first mixed solution.

A second mixed solution was prepared by placing 0.125 g (0.35 mmol) ofneodymium chloride hydrate in a 250 ml round flask, and then adding 20ml of hexane and 10 ml of ethanol thereto to dissolve the neodymiumcompound.

The first mixed solution was introduced to a dropping funnel and wasdropped to the second mixed solution at room temperature (20±5° C.) toprepare a third mixed solution. After completing the addition, theresult was stirred for 15 hours at room temperature (20±5° C.)

The third mixed solution was vacuum distilled to remove all the solvent,50 ml of hexane and 50 ml of distilled water were added to the thirdmixed solution, the result was introduced to a separatory funnel, andthe organic layer was extracted repeating 3 times. Sodium sulfate wasadded to the collected organic layer, the result was stirred for 10minutes at room temperature (20±5° C.), and then the solution obtainedfrom filtration was removed by vacuum distillation. As a result, 0.38 g(yield 94%) of title compound (I), which is yellow and blue solid,dissolved in hexane was obtained.

FT-IR: u 953, 2921, 2852, 1664, 1557, 1505, 1457, 1412, 1377, 1311, 1263cm⁻¹

PREPARATION EXAMPLE 2: SYNTHESIS OF ND(NEODECANOATE)₃

To a 100 ml round flask having 4.32 g (25 mmol) of neodecanoic acidtherein, 100 ml of ethanol was added, and the result was stirred for 10minutes at room temperature (20±5° C.). 25 ml of a 1.0 M aqueous sodiumhydroxide solution (25 mmol) was added to this solution, and the resultwas stirred for 1 hour at room temperature (20±5° C.) to prepare a firstmixed solution.

A second mixed solution was prepared by placing 3.0 g (8.3 mmol) ofneodymium chloride hydrate in a 500 ml round flask, and then adding 150ml of hexane and 100 ml of ethanol thereto to dissolve the neodymiumcompound.

The first mixed solution was introduced to a dropping funnel and wasdropped to the second mixed solution at room temperature (20±5° C.) toprepare a third mixed solution. After completing the addition, theresult was stirred for 15 hours at room temperature (20±5° C.)

The third mixed solution was vacuum distilled to remove all the solvent,100 ml of hexane and 100 ml of distilled water were added to the thirdmixed solution, the result was introduced to a separatory funnel, andthe organic layer was extracted repeating 3 times. Sodium sulfate wasadded to the collected organic layer, the result was stirred for 10minutes at room temperature (20±5° C.), and then the solution obtainedfrom filtration was removed by vacuum distillation. As a result, 5.3 g(yield: 96%) of a title compound (II), which is purple solid, wasobtained.

FT-IR: u 956, 2926, 2872, 1512, 1462, 1411, 1375, 1181, 641 cm⁻¹

[Preparation of Conjugated Diene-Based Polymer]

EXAMPLE 1

Step (i): Preparation of Molecular Weight Modifier and ConjugatedDiene-Based Monomer Mixture

Vacuum and nitrogen were alternately applied to a completely dried 10 Lhigh pressure reactor, and an atmospheric pressure (1±0.05 atm) statewas made by filling the reactor with nitrogen again. To this highpressure reactor, hexane (2086.4 g) and 1,3-butadiene (250 g) were addedand mixed, and first heat treatment was carried out for approximately 10minutes at 70° C. Diisobutylaluminum hydride (DIBAH) was added and mixedto this high pressure reactor in an amount listed in the following Table1, the resultant mixed solution was second heat treated forapproximately 2 minutes at approximately 70° C. to prepare a mixture ofa molecular weight modifier and a conjugated diene-based monomer.

Step (ii): Polymerization Reaction

The neodymium compound of Preparation Example 1, modifiedmethylaluminoxane (MMAO)(MISC MAO, Lot: 9578-110-3, AlbemarleCorporation, Al content in isoheptane=8.6% by weight) and hexane werepremixed in amounts listed in the following Table 1, and then the resultwas heat treated for minutes at 50° C. To the resultant mixture,diethylaluminum chloride (DEAC) was added in an amount listed in thefollowing Table 1, and the result was heat treated for 10 minutes at 26°C. to prepare a catalyst composition.

To the mixture of the molecular weight modifier and the conjugateddiene-based monomer prepared in the step (i), the catalyst compositionwas injected, and a polymerization reaction was carried out for 40minutes at 70° C. to obtain 1,4-cis polybutadiene.

EXAMPLE 2

1,4-Cis polybutadiene was prepared in the same manner as in Example 1except that the neodymium compound prepared in Preparation Example 1,the MMAO, the hexane, the DIBAH and the DEAC were used in amounts listedin the following Table 1.

EXAMPLES 3 AND 4

1,4-Cis polybutadiene was prepared in the same manner as in Example 1except that the neodymium compound prepared in Preparation Example 2 wasused instead of the neodymium compound prepared in Preparation Example1, and the neodymium compound of Preparation Example 2, the MMAO, thehexane, the DIBAH and the DEAC were used in amounts listed in thefollowing Table 1.

EXAMPLES 5 TO 7

1,4-Cis polybutadiene was prepared in the same manner as in Example 1except that the neodymium compound prepared in Preparation Example 2 wasused instead of the neodymium compound prepared in Preparation Example1, and the polymerization reaction was carried out for approximately 40minutes at a polymerization reaction temperature of 30° C. using theneodymium compound of Preparation Example 2, the MMAO, the hexane, theDIBAH and the DEAC in amounts listed in the following Table 2.

COMPARATIVE EXAMPLE 1

Vacuum and nitrogen were alternately applied to a completely dried 10 Lhigh pressure reactor, and an atmospheric pressure state was made byfilling the reactor with nitrogen again. To this high pressure reactor,hexane (2086.4 g) and 1,3-butadiene (250 g) were added and mixed, andfirst heat treatment was carried out for approximately 10 minutes at 70°C. A solution mixing the neodymium compound of Preparation Example 1,DIBAH and DEAC in amounts listed in the following Table 1 was added tothis high pressure reactor, and the result was polymerization reactedfor 30 minutes at 70° C. to prepare 1,4-cis polybutadiene.

COMPARATIVE EXAMPLE 2

1,4-Cis polybutadiene was prepared in the same manner as in ComparativeExample 1 except that the neodymium compound prepared in PreparationExample 2 was used instead of the neodymium compound prepared inPreparation Example 1, and the neodymium compound of Preparation Example2, the hexane, the DIBAH and the DEAC were used in amounts listed in thefollowing Table 1, and the reaction was carried out under a conditionlisted in Table 1.

COMPARATIVE EXAMPLES 3 AND 4

1,4-Cis polybutadiene was prepared in the same manner as in ComparativeExample 1 except that the neodymium compound prepared in PreparationExample 2 was used instead of the neodymium compound prepared inPreparation Example 1, and the neodymium compound of Preparation Example2, the hexane, the DIBAH and the DEAC were used in amounts listed in thefollowing Table 2, and the reaction was carried out under a conditionlisted in Table 2.

TEST EXAMPLE 1: EVALUATION ON CONVERSION RATE AND CATALYTIC ACTIVITY

After completing the polymerization reaction for preparing 1,4-cispolybutadiene in the examples and the comparative examples, some of thereaction solution was taken to measure a conversion rate, and catalyticactivity was calculated based on the conversion rate.

In detail, the conversion rate was calculated using a ratio of a valuemeasuring the mass of some of the reaction solution taken aftercompleting the polymerization reaction, and a value measuring the massof polybutadiene remaining after removing all the hexane solvent andresidual butadiene by heating the some of the polymer for 10 minutes at120° C.

In addition, catalytic activity was calculated based on the conversionrate using the mass of the produced polybutadiene, the number of mol ofthe neodymium compound used in the polymerization reaction, and thepolymerization time. The results are shown in the following Tables 1 and2.

TEST EXAMPLE 2: EVALUATION ON PHYSICAL PROPERTY

Physical properties of each 1,4-cis polybutadiene prepared in theexamples and the comparative examples were measured as follows, and theresults are shown in the following Tables 1 and 2.

1) Weight Average Molecular Weight (Mw), Number Average Molecular Weight(Mn) and Polydispersity (PDI)

The 1,4-cis polybutadiene prepared in the examples and the comparativeexamples was each dissolved for 30 minutes in tetrahydrofuran (THF)under a condition of 40° C., and was loaded and passed through gelpermeation chromatography (GPC). Herein, two PLgel Olexis (trade name)columns and a PLgel mixed-C column manufactured by Polymer Laboratorieswere combined and used as the column. In addition, mixed bed-typecolumns were all used as the newly replaced column, and polystyrene wasused as a gel permeation chromatography (GPC) standard material.

2) Mooney Viscosity and −S/R Value

For the 1,4-cis polybutadiene prepared in the examples and thecomparative examples, Mooney viscosity (MV) was measured using a LargeRotor of MV2000E manufactured by Monsanto under a condition of RotorSpeed 2±0.02 rpm at 100° C. Herein, the used sample was left unattendedfor 30 minutes or longer at room temperature (23±5° C.), 27±3 g thereofwas collected, and inside a die cavity is filled with the sample, andMooney viscosity was measured while operating a Platen and applyingTorque.

In addition, changes in the Mooney viscosity appearing while releasingTorque were observed when measuring the Mooney viscosity, and the −S/Rvalue was determined from the slope.

3) Cis-1,4 Bond Content

For the 1,4-cis polybutadiene prepared in the examples and thecomparative examples, Fourier Transform Infrared Spectroscopy analyseswere carried out, and cis-1,4 bond content in the 1,4-cis polybutadienewas obtained from the results.

TABLE 1 Molecular Weight Modifier- Containing Mixture CatalystComposition Preparation Polymerization Preparation¹⁾ Nd-Based ReactionConversion DIBAH Compound MMAO DEAC Hexane DIBAH Temperature Time Rate(mmol) (mmol) (mmol) (mmol) (mmol) (mmol) (° C.) (min) (%) Example 10.25 Preparation 3.0 0.18 80 — 70 10 100 Example 1 0.08 Example 2 0.66Preparation 4.0 0.18 80 — 70 10 100 Example 1 0.05 Example 3 1.0Preparation 1.2 0.09 40 — 70 10 100 Example 2 0.04 Example 4 1.0Preparation 0.8 0.09 40 — 70 10 100 Example 2 0.04 Comparative —Preparation — 0.55 120 3.0 70 30 88 Example 1 Example 1 0.24 Comparative— Preparation — 0.55 120 3.0 70 30 86 Example 2 Example 2 0.24 PhysicalProperty Evaluation Catalytic Cis-1,4 Activity Bond [kg [polymer]/ Mn MwContent mol[Nd] · h (×10³ g/mol) (×10³ g/mol) FDI MV −S/R (%) Example 113,194 8.9 22.2 2.5 55.6 1.0521 96.8 Example 2 13,194 6.7 15.9 2.38 75.71.0456 96.2 Example 3 26,335 4.3 9.9 2.31 43.5 1.0423 98.4 Example 426,335 4.2 10.2 2.41 59.6 1.0786 98.5 Comparative 733 1.9 6.2 3.24 46.00.6529 96.4 Example 1 Comparative 717 2.1 9.0 4.34 45.5 0.8556 97.3Example 2

TABLE 2 Molecular Weight Modifier- Containing Mixture CatalystComposition Preparation Polymerization Preparation¹⁾ Nd-Based ReactionConversion DIBAH Compound MMAO DEAC Hexane DIBAH Temperature Time Rate(mmol) (mmol) (mmol) (mmol) (mmol) (mmol) (° C.) (min) (%) Example 50.92 Preparation 8.0 0.18 80 — 30 40 100 Example 2 0.08 Example 6 0.87Preparation 8.0 0.18 80 — 30 40 100 Example 2 0.08 Example 7 0.83Preparation 5.0 0.18 80 — 30 40 100 Example 2 0.08 Comparative —Preparation — 0.46 100 2.04 70 60 96 Example 3 Example 2 0.20Comparative — Preparation — 0.46 100 1.82 70 60 91 Example 4 Example 20.20 Physical Property Evaluation Catalytic Cis-1,4 Activity Bond [kg[polymer]/ Mn Mw Content mol[Nd] · h (×10³ g/mol) (×10³ g/mol) FDI MV−S/R (%) Example 5 4,688 3.1 7.4 2.35 39.5 1.0906 96.0 Example 6 4,6883.2 8.0 2.48 46.1 1.0122 95.6 Example 7 4,688 3.4 8.3 2.41 50.5 1.044696.1 Comparative 1,200 2.0 6.3 3.06 33.5 0.8563 96.5 Example 3Comparative 1,318 2.4 7.7 3.28 43.8 0.8548 97.4 Example 4

In Tables 1 and 2, preparation of a mixture containing a molecularweight modifier of 1) means preparation of a mixture by mixing amolecular weight modifier and a diene-based monomer.

Table 1 compares polymer conversion rates, catalytic activity, andcis-1,4 bond content in the prepared polymers, molecular weightdistribution and linearity depending on the content of the MMAO and theDIBAH, and the order of the DIBAH introduction.

As can be seen from Table 1, the polymers of Examples 1 to 4 exhibitedsignificantly enhanced polymer conversion rates and catalytic activity.

When specifically examined, in Examples 1 to 4, the polymerization timewas reduced to ⅓ at the same polymerization temperature even when usingthe Nd-based main catalyst compound in a small amount of approximately ⅙to ⅓ compared to Comparative Examples 1 and 2. In addition, in Examples1 to 4, a 100% polymer conversion rate was obtained even when reducingthe amount of the main catalyst and the polymerization time. Meanwhile,in Comparative Examples 1 and 2, low polymer conversion rates ofapproximately 86% to 88% were obtained despite that the amount of themain catalyst increased by 3 times to 6 times, and the polymerizationtime increased by 3 times compared to Examples 1 to 4.

In addition, in Examples 1 to 4, catalytic activity was enhanced up to15 times to 35 times when compared to Comparative Examples 1 and 2.

Furthermore, the 1,4-cis polybutadiene prepared in Examples 1 to 4exhibited narrower molecular weight distribution compared to ComparativeExamples 1 and 2. Specifically, whereas the 1,4-cis polybutadiene ofExamples 1 to 4 had PDI in a range of 2.3 to 2.5 with a molecular weightdistribution range of 2.5 or less, the polymers of Comparative Examples1 and 2 had PDI of 3.24 and 4.34, respectively, and exhibitedsignificantly increased molecular weight distribution compared toExamples 1 to 4.

In addition, Table 2 compares polymer conversion rates, catalyticactivity, and cis-1,4 bond content in the prepared 1,4-cispolybutadiene, molecular weight distribution and linearity depending onthe order of the DIBAH introduction while varying the DIBAH content andthe polymerization temperature.

Specifically, as can be seen from Table 2, Examples 5 to 7 had very highcatalytic activity, and polymerization was readily carried out in ashort period of time even at a low temperature (30° C.). Meanwhile, inComparative Examples 3 and 4, the polymerization conversion rate did notreach 100% even when polymerization was carried out for 60 minutes at70° C.

In addition, the 1,4-cis polybutadiene prepared in Examples 5 to 7 had−S/R of 1 or greater, a value increased by 20% or greater compared toComparative Examples 3 and 4. From this result, it may be predicted thatthe 1,4-cis polybutadiene of Example 5 to 7 had very high linearity, andas a result, when used in tires, rolling resistance declines and fuelefficiency properties are capable of being enhanced.

1. A method for preparing a conjugated diene-based polymer comprising:preparing a mixture of a molecular weight modifier and a conjugateddiene-based monomer; and polymerization reacting the mixture using acatalyst composition including a lanthanide rare earthelement-containing compound, modified methylaluminoxane, a halogencompound and an aliphatic hydrocarbon-based solvent.
 2. The method forpreparing a conjugated diene-based polymer of claim 1, wherein thecatalyst composition is prepared by mixing the lanthanide rare earthelement-containing compound, the modified methylaluminoxane, the halogencompound and the aliphatic hydrocarbon-based solvent, and then heattreating the result in a temperature range of 0° C. to 60° C.
 3. Themethod for preparing a conjugated diene-based polymer of claim 1,wherein the catalyst composition is prepared by mixing the lanthaniderare earth element-containing compound, the modified methylaluminoxaneand the aliphatic hydrocarbon-based solvent, first heat treating theresult in a temperature range of 10° C. to 60° C., introducing thehalogen compound to the resultantly obtained product, and second heattreating the result in a temperature range of 0° C. to 60° C.
 4. Themethod for preparing a conjugated diene-based polymer of claim 1,wherein the catalyst composition includes the lanthanide rare earthelement-containing compound in an amount of 0.01 mmol to 0.25 mmol withrespect to 100 g of the conjugated diene-based monomer.
 5. The methodfor preparing a conjugated diene-based polymer of claim 1, wherein thecatalyst composition includes the lanthanide rare earthelement-containing compound in 0.01 mmol to 0.25 mmol, the modifiedmethylaluminoxane in 0.05 mmol to 50.0 mmol, the halogen compound in0.01 mmol to 2.5 mmol, and the aliphatic hydrocarbon-based solvent in 5mmol to 200 mmol with respect to 100 g of the conjugated diene-basedmonomer.
 6. The method for preparing a conjugated diene-based polymer ofclaim 1, wherein, in the modified methylaluminoxane, 50 mol % to 90 mol% of a methyl group of the methylaluminoxane is substituted with ahydrocarbon group having 2 to 20 carbon atoms.
 7. The method forpreparing a conjugated diene-based polymer of claim 6, wherein thehydrocarbon group is a linear or branched alkyl group having 2 to 10carbon atoms.
 8. The method for preparing a conjugated diene-basedpolymer of claim 1, wherein the modified methylaluminoxane includestrimethylaluminum; and a mixed alkyl group derived from one or moretypes of trialkylaluminums other than trimethylaluminum, and thetrialkylaluminum may include any one or a mixture of two or more typesselected from the group consisting of triisobutylaluminum,triethylaluminum, trihexylaluminum and trioctylaluminum.
 9. The methodfor preparing a conjugated diene-based polymer of claim 1, wherein thelanthanide rare earth element-containing compound includes a neodymiumcompound of the following Chemical Formula 1:

wherein, in Chemical Formula 1, R₁ to R₃ are each independently ahydrogen atom, or a linear or branched alkyl group having 1 to 12 carbonatoms.
 10. The method for preparing a conjugated diene-based polymer ofclaim 9, wherein the lanthanide rare earth element-containing compoundincludes a neodymium compound in which, in Chemical Formula 1, R₁ is alinear or branched alkyl group having 6 to 12 carbon atoms, and R₂ andR₃ are each independently a hydrogen atom or a linear or branched alkylgroup having 2 to 8 carbon atoms, but R₂ and R₃ are not both hydrogenatoms at the same time.
 11. The method for preparing a conjugateddiene-based polymer of claim 9, wherein the lanthanide rare earthelement-containing compound includes a neodymium compound in which, inChemical Formula 1, R₁ is a linear or branched alkyl group having 6 to 8carbon atoms, and R₂ and R₃ are each independently a linear or branchedalkyl group having 2 to 8 carbon atoms.
 12. The method for preparing aconjugated diene-based polymer of claim 1, wherein the lanthanide rareearth element-containing compound includes any one or a mixture of twoor more selected from the group consisting of Nd(2,2-diethyldecanoate)₃, Nd(2,2-dipropyl decanoate)₃, Nd(2,2-dibutyl decanoate)₃,Nd(2,2-dihexyl decanoate)₃, Nd(2,2-dioctyl decanoate)₃,Nd(2-ethyl-2-propyl decanoate)₃, Nd(2-ethyl-2-butyl decanoate)₃,Nd(2-ethyl-2-hexyl decanoate)₃, Nd(2-propyl-2-butyl decanoate)₃,Nd(2-propyl-2-hexyl decanoate)₃, Nd(2-propyl-2-isopropyl decanoate)₃,Nd(2-butyl-2-hexyl decanoate)₃, Nd(2-hexyl-2-octyl decanoate)₃,Nd(2-t-butyl decanoate)₃, Nd(2,2-diethyl octanoate)₃, Nd(2,2-dipropyloctanoate)₃, Nd(2,2-dibutyl octanoate)₃, Nd(2,2-dihexyl octanoate)₃,Nd(2-ethyl-2-propyl octanoate)₃, Nd(2-ethyl-2-hexyl octanoate)₃,Nd(2,2-diethyl nonanoate)₃, Nd(2,2-dipropyl nonanoate)₃, Nd(2,2-dibutylnonanoate)₃, Nd(2,2-dihexyl nonanoate)₃, Nd(2-ethyl-2-propyl nonanoate)₃and Nd(2-ethyl-2-hexyl nonanoate)₃.
 13. The method for preparing aconjugated diene-based polymer of claim 1, wherein the aliphatichydrocarbon-based solvent includes any one or a mixture of two or moreselected from the group consisting of linear, branched or cyclicaliphatic hydrocarbon having 5 to 20 carbon atoms.
 14. The method forpreparing a conjugated diene-based polymer of claim 1, wherein thealiphatic hydrocarbon-based solvent includes any one selected from thegroup consisting of hexane, cyclohexane and a mixture thereof.
 15. Themethod for preparing a conjugated diene-based polymer of claim 1,wherein the halogen compound includes any one or a mixture of two ormore selected from the group consisting of elemental halogen compounds,interhalogen compounds, halogenated hydrogen, organic halides, non-metalhalides, metal halides and organic metal halides.
 16. The method forpreparing a conjugated diene-based polymer of claim 1, wherein thecatalyst composition includes the modified methylaluminoxane in a molarratio of 5 to 200 with respect to 1 mol of the lanthanide rare earthelement-containing compound.
 17. The method for preparing a conjugateddiene-based polymer of claim 1, wherein the catalyst compositionincludes the modified methylaluminoxane in 5 mol to 200 mol, the halogencompound in 1 mol to 10 mol and the aliphatic hydrocarbon-based solventin 20 mol to 20,000 mol with respect to 1 mol of the lanthanide rareearth element-containing compound.
 18. The method for preparing aconjugated diene-based polymer of claim 1, wherein the catalystcomposition is a pre-mixture of the lanthanide rare earthelement-containing compound, the modified methylaluminoxane, the halogencompound and the aliphatic hydrocarbon-based solvent.
 19. The method forpreparing a conjugated diene-based polymer of claim 1, wherein thecatalyst composition does not include diisobutylaluminum hydride. 20.The method for preparing a conjugated diene-based polymer of claim 1,wherein the molecular weight modifier includes any one or a mixture oftwo or more selected from the group consisting oftrihydrocarbylaluminum, dihydrocarbylaluminum hydride, hydrogen andsilane compounds.
 21. The method for preparing a conjugated diene-basedpolymer of claim 1, wherein the molecular weight modifier is used in anamount of 1 mol to 100 mol with respect to 1 mol of the lanthanide rareearth element-containing compound.
 22. The method for preparing aconjugated diene-based polymer of claim 1, wherein the polymerizationreaction is carried out in a temperature range of 20° C. to 90° C. 23.The method for preparing a conjugated diene-based polymer of claim 1,wherein the polymerization reaction is carried out for 5 minutes to 60minutes until the reaction reaches 100% conversion to the conjugateddiene-based polymer.
 24. The method for preparing a conjugateddiene-based polymer of claim 1, wherein the conjugated diene-basedpolymer is 1,4-cis polybutadiene.
 25. A conjugated diene-based polymerprepared using the method of claim 1, and having 95% or highercis-1,4-bond content.